Material cutting machine and sound-absorbing hood therefor

ABSTRACT

The invention is a machine for comminuting material in which a rotary cutting mechanism is used. A hood is mounted on the machine adjacent the inlet passage thereto, the function of the hood being to minimize the noise caused by the machine when it cuts material. Throughout the machine, additional sound-absorbing means are used at strategic locations to eliminate or minimize the passage of sound from the inside of the total enclosure of the machine to the outside thereof.

Feb. 22, 1972 United States Patent Peterson, Jr.

.....24l/285 B Smith.................................24l/285 R 1541MATERIAL CUTTING MACHINE AND 3,419,223 12/1968 Morin...............

SOUND-ABSORBING HOOD THEREFOR 3,589,624 /1971 [72] Inventor: Russell 1.Peterson, Jr., Seekonk, Mass.

Assignee: Cumberland Engineering Company Inc., Primary Examiner PPawtucket, R1, Attorney-Kenway, .lenney & Hildreth Aug. 12, 19 10 [57]ABSTRACT The invention is a machine for comminuting material in which[22] Filed:

[21] Appl. No.: 63,066

a rotary cutting mechanism is used. A hood is mounted on the thefunction of the ..241/100, 241/286 B, 241/301 machine adjacent the inletpassage thereto,

. ...B02c 23/00, B02 18/00 hood being to minimize the noise caused bythe machine when .241/100, 101 R, 185 R, 186 R, it cuts material.Throughout the machine, additional sound- 286 A, 286 B, 301 absorbingmeans are used at strategic locations to eliminate or [52] US. CL...[51] Int. [58] Field of Search..............

minimize the passage of sound from the inside of the total enclosure ofthe machine to the outside thereof.

[56] References Cited UNITED STATES PATENTS 12 Claims, 4 Drawing FiguresHess et PAIENTEUFEB 22 I972 SHEET 1 OF 2 FIG 2 FIG. 3

INVENTOR RUSSELL I. PETERSON,JR.

ATTORNEYS PAIENTEDFEB2ZIQTZ 3.643.880 SHEET 2 OF 2 FIG 4 INVENTORRUSSELL l. PETERSONJR ATTORNEYS MATERIAL CUTTING MACHINE AND SOUND-ABSORBING HOOD THEREFOR BACKGROUND OF THE INVENTION The invention hasparticularly to do with machines called granulators that are used tochop up or comminute plastic materials. Such machines create a greatdeal of noise. The reason for the noise is that many of the plasticsused today are very tough, and when they are comminuted, the cuttingaction is very noisy due to the kind of knives used. In addition, due tothe rotary action of the cutting means, hard particles of plastic arethrown with some force against the steel walls of the machine withresulting noise.

Attempts have been made to fashion sound-absorbing hoods for suchmachines, and to assemble a combination of the sound-absorbing hood andthe machine which would be convenient to use and which would permitready access to the working parts of the machine without having to liftthe hood therefrom. Such hoods generally are made of extremely thickmetal for the purpose of avoiding vibration of the material when struckby the particles of plastic inside the machine, metal being used towithstand the abrasion of the thrown particles. Such constructions haveserious drawbacks in that when such a hood is made of very thickmaterial it requires a crane or hoist to remove it from the machine inorder to have access to the interior working parts thereof. As a result,while such hoods have been made, they are not considered to be verypractical or economical.

In addition, it has been known that material such as clay and epoxycoatings on metal, soft metals such as lead and aluminum, and the foamedplastics all have an ability to absorb or attenuate sound impingingthereon to some degree. Such materials have been used, but it has beenfound that when so used in what would be considered the normal manner,the noise level of the machine was reduced but not sufficiently to havemuch significance.

It has been said that 90 percent of noise created in the interior of anoisy machine will exit from an opening in the machine amounting to onlypercent of a covering for the machine. This factor creates the problemof how to feed scrap material into machines which have noise suppressionhoods associated therewith, because feeding the materials into themachine must be done through an opening, with the result that interiornoise will escape through the feed opening. Using screens to mask thefeed opening will help, but is not enough.

Therefore, it is the general purpose of this invention to provide amachine and enclosure therefor having the following important objectivesand characteristics:

One object of the invention is to provide an enclosure for a cuttingmachine, in which the enclosure is double-walled, and so made that noiseis significantly attenuated and absorbed before it can reach the outsideof the machine and the enclosure.

Another object of the invention is to provide a combined enclosure andfeed hopper for a cutting machine which can be easily attached to amachine so as to be movable with respect thereto, the combinedenclosure-hopper being so mounted on the machine that a single man ofnormal strength can move the enclosure and feed hopper with respect tothe machine so that ready access to the interior of the machine can behad for maintenance purposes.

Still another object of the invention is to provide apparatus of theaforementioned kinds, in which the materials used to absorb andattenuate the sound of the machine can be readily attainable on the openmarket at cost which is not prohibitively expensive.

Another object of the invention is the provision of a combined enclosureand feed hopper of any of the abovedescribed kinds, as well as amaterial receiving hopper therefor, can be readily fabricated,-inaccordance with the instructions of this disclosure, in any averagemachine shop which has equipment suitable for fabricating articles outof sheet and plate metals.

Other objects and advantages will be in part obvious and in part pointedout hereinafter.

The invention accordingly comprises the elements and combinations ofelements, features of construction, arrangements of parts, andmanipulation of the apparatus all of which will be exemplified in thestructures hereinafter set forth, and the scope of the application ofwhich will be indicated in the appended claims.

In the accompanying drawings, in which one of the various possibleembodiments of the invention is illustrated:

FIG. I is a perspective view of the combined enclosure and hopper ofthis invention attached to the base of a material cutting machine. (Inthis drawing, the motor that drives the machine has been deleted forpurposes of clarity.)

FIG. 2 is a vertical cross-sectional view of the machine, with certainparts cut away in order to illustrate the general interior constructionof both the machine and the combined enclosure and feed hopper thereof.In this view, a second position of the combined enclosure-feed hopper isshown.

FIG. 3 is a vertical elevation of a portion of the above embodiment ofthis invention, and is given to show a motor in place, with certainsound-absorbing and attenuating means being provided in connection withthe drive pulley mounted on the shaft of the motor.

FIG. 4 is a sectional plan view of the combined enclosure and feedhopper ofthis invention, taken in the direction of sight lines 4-4 onFIG. 2, the view being given in orderto illustrate the construction ofthe walls of the outer enclosure and the walls of the inner feed hopper.

Similar reference characters indicate corresponding parts throughoutseveral views of the drawing. In the drawings, dimensions of certain ofthe parts as shown may have been modified and/orexaggerated for thepurposes of clarity of illustration and understanding the invention.

Referring now to FIGS. 1 and 2, there is illustrated one embodiment ofthis invention comprising a material cutting machine indicated generallyby numeral 2, the machine having a base 4 within which is mounted arotary cutting mechanism indicated generally by numeral 6, and an inlet8 and outlet 10. Such a machine is one which is built, for example, byCumberland Engineering Company Inc. of Pawtucket R.I., and isillustrated in Bulletin No. 700 of that company, for example, Model 2Granulator using a 10 motor at 1,800 rpm. It will be noted that theinlet 8 is at the upper side of the granulator and the exit 10 is at thelower, so that material is fed into the granulator from the topdownwardly. Mounted on the base 4 is an electrical motor 12 (see FIG. 2)mounting being done by customary bolts on the mounting plate 14 which isalso conventional. The motor is provided with a shaft 16, as is usual,and at the end of the shaft 16 is mounted the multiple groove V-pulley18 which is used to drive the cutting mechanism 6 by means of a similarmultiple groove V-pulley 20 mounted at the end of the rotary cutter ofthe machine.

Mounted on top of the base 4 is the combined enclosurefeed hopperstructure of this invention, indicated generally by numeral 26. Thestructure 26 is hinged on the base 4, for example, by the pivots 28, oneon each side of the 'base and, respectively, the sidewalls of theenclosure, suitable lugs being provided on the sidewalls of the base andthe sidewalls of the enclosure for the purpose. Since the constructionof the pivots is conventional, no further description will be given. Ofcourse, if desired, other means of hinging or pivoting the enclosure 26on the base can be provided.

The purpose of hinging the base is so that, as shown by the dot-dashlines in FIG. 2, the enclosure 26 may be swung to the position 30 asshown in FIG. 2. It will be observed that the shape of the combinedenclosure and hopper is such that the entire structure is well balancedon the pivots or hinge 28. Therefore, even though the structure maybeheavy, it can be easily moved from the full line position shown inFIG. 2, to the dotted line position by a man of ordinary strength.However, in the full line position shown in FIG. 2, the enclosure 26 isseated firmly on the slanting upper table 32 of the base.

As illustrated in FIGS. 2 and 4, the structure 26 is constructed asfollows: Speaking first of the outer enclosure, it has in general aninverted L-shape, with the horizontally extending arm 34 and anapproximately vertical leg portion 36. The enclosure has sidewalls 38and 40, backwall 42, and front wall 44. Each of the walls has aplural-layered construction, in which the outermost first layer is asound attenuation material, and the inner layers are sound-absorptionand sound attenuation material. As an example of the respectivematerials, the outermost layer of wall 38, for example, is a sheet ofaluminum 46, this being selected because of its inert characteristics sofar as vibrations are concerned. Other materials could be used, forexample, such as brass or copper, but it is felt that the aluminumprovides the sound attenuation required and yet at the same time islight and provides sufficient strength and rigidity to maintain theshape of the outer enclosure. The outer layers of all of the walls ofthe enclosure are similarly made of sheet aluminum. Next in order,inwardly, is a layer of foamed absorbing material 48 in each wall, nexta layer of metallic lead 50, and finally an innermost layer of foamedabsorbing material 52. The lead layer 50 acts as a damping and soundattenuating layer, and the two foamed layers 48 and 52 constitutesound-absorbing layers. It is preferred that the foamed layers 48 and 52be of polyurethane foam, but other foamed synthetic artificial plasticresins may be used if desired. The layers 48, 50 and 52 are preferablyfastened together by suitable adhesive and this combination is thenpreferably fastened to the layer 46 by a suitable adhesive. A suitableadhesive may be, for example, a contact cement such as an epoxy resin,any number of which are commonly available on the market.

As an example of the thicknesses of the relative layers, the layer ofaluminum 46 may be approximately 0.092 inches thick; the layer of foammaterial 48 may be approximately one-fourth inch thick; the layer oflead may be approximately one-thirtysecond inch thick; and the innermostlayer of polyurethane foamed material may be approximately 1 inch thick.(Material such as that comprising the three layers 48, 50 and 52 may bepurchased from the Sound Coat Co., l5 Madison Avenue, New York, NY.10022, if desired.) Walls 42, 40 and 44 are the same as that describedfor wall 38.

Front wall 44 has an opening 56 provided therein adapted to align withthe front end opening 58 of the interior hopper indicated generally bynumeral 60. A rectangularly shaped sleeve 62 is inserted within theopening 56 and also within the opening 58, the sleeve having an exteriorflange 64 by means of which it is fastened to the aluminum face of thefront wall 44 in conventional manner by means of the screws 66. Theinterior end of the sleeve serves to hold the end of the hopper 60 inposition with respect to the opening 56in the front wall 44.

Like the enclosure 26, the hopper 60 is also L-shaped, and comprises arectangular tubular structure having the sidewalls 70 and 72, backwall74, bottom 76, top 77 and vertical front wall 78. As a result of thisconstruction, the hopper resembles to a great extent the shape of theoutside enclosure 26, except that it is smaller. The outer surfaces ofthe hopper are coated with a sound attenuating material 61 which is aclay-epoxy resin mixture purchasable, if desired, from the Sound CoatC0. and sold as GP I material; or if desired, the layer 61 may bevermiculite.

The entire hopper thus fits approximately centrally within the enclosure26, and is held spaced therefrom by suitable brackets 80 which extendfrom the enclosure 26 to the hopper. The exact location of thesebrackets is not critical, and their function is simply to space thehopper from the enclosure.

Attached to the lower or inner end of the hopper 60 are the reinforcingplates 82 which surround the hopper on all four sides. Thesereinforcements are made of heavy sheet metal, and are attached bywelding or riveting to the hopper walls. The purpose of having thereinforcements is to strengthen the hopper and stiffen it, particularlysince it is against the bottom or inner end of the hopper that particlesmay be thrown by the rotatingcutting machine with considerable force.The perimeter of the hopper at the bottom is so shaped that when theenclosure 26 is in the position (upright) as shown in FIG. 2, the

perimeter rests adjacent the plane defining the inlet passage 8 of thegranulator 6.

From the construction, it is clear that material is fed into the machinevia hopper 60 and then falls by gravity into the granulator. In view ofthe fact that a very large amount of sound would exit from the interiorof the machine through the upper horizontal throat of the hopper 60,unless this is blocked off, it is necessary to close this throat butstill allow material to be fed into the granulator through thispassageway. Therefore, means are provided to block off the noise. Thisis done conveniently by a plurality of flexible sheet material curtains86, each curtain comprising two flexible elastomeric sheets 88 and 90,such as Neoprene, which are fastened to the top of the hopper byconventional means such as the straps 92. The curtains hang downwardlyuntil they almost touch the bottom floor 76 of the hopper. The membersof each pair hang closely together. Thus, since the curtains areflexible and freely swinging, material may be introduced into the upperhorizontal leg of the hopper and once the material is introduced, thecurtains then again hang down and block any noise trying to emerge fromthe hopper. One or more of the curtains may be, if desired, impregnatedwith lead particles.

The members of the pair of curtains 86 at the entrance of the hopper maybe fastened thereto by the framework 92 which is suitably held againstthe sleeve 62 by the screws 66. The attachment of the curtains to thehopper is conventional, no further description will be given herein.

At the lower end of the backwall 36 of the enclosure there is provided aslot 94 open at its bottom end. Mounted on the base 4 is a pulleyandbelt-shrouding member 96 whose inner end 98 extends within theenclosure. The shroud 96 is detachably fastened to base 4. A softflexible gasket 100 surrounds the edge of the slot, so that when theenclosure is in the position shown in FIG. 1, there is a basicallysoundtight seal between the enclosure and the shroud 96. A hole 102 isprovided in the wall of the shroud and is adapted to receivetherethrough the shaft 16 of the motor.

One function of shroud 96 is to enclose V-pulley l8 and the transmissionbelts 22, in order to protect any user of the machine from becomingentangled with the drive means. A second purpose of the shroud is toprovide a sound barrier, and it may, if desired, have a coating on theinside thereof equivalent to the coating 61 which is on the outside ofthe hopper walls. The effect of such a coating will be to dampen anyvibrations of the shroud 96, but the problem of sound emerging from thehole 102 still remains/This matter is taken care of in this invention byincluding snugly between the end 104 of the motor frame and the wall ofthe enclosure (see FIG. 3), a resilient pad 106 of cushioning materialwhich blocks off the emergence of any sound from the hole 102. The fitof pad 106 around shaft 16 is a running fit, preferably.

The material of the sound-absorbing cushion 106 preferably is a foamedpolyurethane synthetic plastic resin, such as is used for the layer 52.Or, if desired, the cushion 106 can be a composite layer such as thetotal layer 48,50,52 as shown in FIG. 4, That is, the cushion 106 can bea layer of polyurethane foam approximately one-fourth inch thick, then alayer of lead approximately one-thirtysecond inch thick, and finallyanother layer of polyurethane foam approximately 1 inch thick.

By the construction thus described, the enclosure 26 may be swung aboutthe pivot points 28 to the position shown by the dot-dash lines 30 inFIG. 2, and as it so swings the open end of the slot 94 will permit thebottom end of the enclosure 26 to escape from the belt shroud 96.

In the position shown in FIG. 2 in full lines, that is, the uprightposition, the enclosure 26 is securely anchored to the base 10 by meansof Iatchbolts 106 which extend through the eyes 108 fastened to wall 42,nuts being provided for conventional anchoring purposes.

Referring to FIG. 2, there is shown in dotted lines a bin 110 ofconventional structure, which is attached to the bed of the cuttingmachine adjacent the exit 10 thereof. The bin is preferably a four-sidedstructure having conventional walls, and at the open end of the binthere is provided a flange 112 which surrounds the periphery of thisopen end. The flange, when the bin is positioned, seats itself firmlyagainst the underside of the bed 32, and the bin is clamped intoposition by means of the fixed bracket 114 and the movable dog [16 whichmay be loosened andturned in order to remove the bin. If desired, butnot shown, suitable gasketing material may be mounted between the flange112 of the bin and the base of the bed 32.

in view of the above, it will be seen that the several objects areachieved, and other advantageous results attained.

it is to be understood that the invention is not limited in itsapplication to the details of construction and arrangement of partsillustrated in the accompanying drawings, since the invention is capableof other embodiments and of being practiced or carried out in variousways. Also, it is to be understood that the phraseology or terminologyemployed herein is for the purpose of description and not of limitation.

As many changes could be made in the above constructions withoutdeparting from the scope of the invention, it is intended that allmatter contained in the above description or shown in the accompanyingdrawings, shall be interpreted as illustrative and not in a limitingsense, and it is also intended that the appended claims shall cover allsuch equivalent variations as come within the true spirit and scope ofthe invention.

Having described the invention, what is claimed is:

l. A sound-absorbing combined hopper and enclosure structure for amachine for cutting materials, the machine having a base, cutting meansmounted on the base, a motor for driving the cutting means, and inletand exit passage means to and from the cutting means, comprising:

an elongated tubular structure having outside and inside compositewalls, the walls being spaced apart to provide an airspace therebetween,the-outer walls forming the enclosure and the inside walls forming thehopper, and including means holding the walls in their spaced relationwhereby the combined outside and inside walls are adapted to movetogether;

the outer composite wall being a plural-layered structure comprising anoutermost first layer of sound attenuation material and inner layers ofsound-absorption material and sound attenuation material; the innercomposite wall comprising at least two layers of material, a firstinnermost layer being of a wear-resistant metal and a second outer layerbeing a sound damping layer, the two layers being attached to eachother; and

said tubular structure being movably hinged to said base with the innerend of said hopper being located adjacent the mouth of said inletpassage, the structure being movable on said hinge to swing away fromsaid inlet passageway and said cutter, thereby to permit access to thelatter.

2. The structure of claim 1 in which the layers of the outer compositewall comprise, in the order named from outside to inside, a layer ofaluminum, a layer of artificial foamed plastic resin, a layer of lead,and a layer of artificial foamed plastic resin.

3. The structure of claim 2 in which the artificial foamed plastic resinis polyurethane.

4. The structure of claim 1 in which the layers of the inner compositewall comprise, in the order named from outside to inside, a layer ofvermiculite, and a layer of steel, the latter being the innermost layerof the hopper.

S. The structure of claim 1 in which the combined enclosure and hopperstructure is generally L-shaped and vertically oriented, one leg of theL-shape extending substantially horizontally, the other leg of theL-shape being connected to the base with the hopper adjacent said inletpassage and including a plurality of sound minimizing curtains in saidhorizontally extending leg attached to the top of the hopper and freelyhanging downwardly toward the bottom of the horizontal section of thehopper, said curtains comprising flexible sheets of an elastomer.

6. The structure of claim 5 in which the layers of the outer compositewall comprise in the order named from outside to inside: a layer ofaluminum, a layer of artificial foamed plastic resin, a layer of lead,and a layer of artificial foamed plastic resin; and the layers of theinnermost composite wall comprise, in the order named from outside toinside, a layer of vermiculite and a layer of steel, and said curtainscomprise a plurality of pairs of curtains, each pair comprising two ofsaid sheets hanging closely adjacent each other.

7. A machine for cutting materials, comprising a base;

cutting means mounted on the base;

a motor for driving the cutting means;

inlet and exit passage means to and from the cutting means;

a sound-absorbing combined enclosure and hopper struc ture, saidstructure comprising:

an elongated tubular structure having outside and inside compositewalls, the walls being spaced apart to provide an airspace therebetween,the outer walls forming the enclosure and the inside walls forming thehopper, and including means holding the walls in their spaced relationwhereby the combined outside and inside walls are adapted to movetogether;

the outer composite wall being a plural-layered structure comprising anoutermost first layer of sound attenuation material and inner layers ofsound-absorption material and sound attenuation material; the innercomposite wall comprising at least two layers of material, a firstinnermost layer being of a wear-resistant metal, and a second outerlayer being a sound damping layer, the two layers being attached to eachother; and

said tubular structure being movably hinged to said base with the innerend of said hopper being located adjacent the mouth of said inletpassage, the structure being movable on said hinge to swing away fromsaid inlet passageway and said cutter, thereby to permit access to thelatter.

8. The machine of claim 7 including a bin removably fastened to saidbase adjacent said exit passage in position to receive material emergingtherefrom, and sound-absorbing means forming a gasket between the edgesof said bin and said base.

9. The machine of claim 7 in which said motor has a shaft and a pulleymounted thereon, said cutting means has a shaft and a pulley mountedthereon, and including a transmission belt connecting said pulleys, andalso including a shroud for said belt and for said pulleys, said shaftpassing through one wall of the shroud, and sound-absorbing materialsnugly fitted between the end of the frame of the motor-and the wall ofsaid shroud where the shaft passes through the wall, thereby to preventthe egress of sound from the interior of said shroud to the outsidethereof.

10. The machine of claim 7 in which the combined enclosure and hopperstructure is generally L-shaped and vertically oriented, one leg of thestructure extending generally horizontally and the other leg of thestructure extending generally vertically and being connected to saidbase with the hopper adjacent said inlet passage, the machine includinga plurality of sound minimizing curtains in said horizontally extendingleg, the curtains being attached to the top of the hopper and freelyhanging downwardly toward the bottom of the horizontal section of thehopper.

11. The machine of claim 10 in which at least one of said curtainscomprising a flexible sheet of synthetic plastic impregnated with leadparticles, and at least one other of said curtains comprising twoflexible layers of sheet elastomeric material attached to the top of thehopper and hanging downwardly adjacent each other.

12. The structure of claim 7 in which the layers of the outer compositewall comprise in the order named from the outside to inside; a layer ofaluminum, a layer of artificial foamed plastic resin, a layer of lead,and a layer of artificial foam plastic resin; and layers of theinnermost composite wall comprise, in the order named from outside toinside, a layer of sound attenuating material and a layer of steel.

1. A sound-absorbing combined hopper and enclosure structure for amachine for cutting materials, the machine having a base, cutting meansmounted on the base, a motor for driving the cutting means, and inletand exit passage means to and from the cutting means, comprising: anelongated tubular structure haviNg outside and inside composite walls,the walls being spaced apart to provide an airspace therebetween, theouter walls forming the enclosure and the inside walls forming thehopper, and including means holding the walls in their spaced relationwhereby the combined outside and inside walls are adapted to movetogether; the outer composite wall being a plural-layered structurecomprising an outermost first layer of sound attenuation material andinner layers of sound-absorption material and sound attenuationmaterial; the inner composite wall comprising at least two layers ofmaterial, a first innermost layer being of a wear-resistant metal and asecond outer layer being a sound damping layer, the two layers beingattached to each other; and said tubular structure being movably hingedto said base with the inner end of said hopper being located adjacentthe mouth of said inlet passage, the structure being movable on saidhinge to swing away from said inlet passageway and said cutter, therebyto permit access to the latter.
 2. The structure of claim 1 in which thelayers of the outer composite wall comprise, in the order named fromoutside to inside, a layer of aluminum, a layer of artificial foamedplastic resin, a layer of lead, and a layer of artificial foamed plasticresin.
 3. The structure of claim 2 in which the artificial foamedplastic resin is polyurethane.
 4. The structure of claim 1 in which thelayers of the inner composite wall comprise, in the order named fromoutside to inside, a layer of vermiculite, and a layer of steel, thelatter being the innermost layer of the hopper.
 5. The structure ofclaim 1 in which the combined enclosure and hopper structure isgenerally L-shaped and vertically oriented, one leg of the L-shapeextending substantially horizontally, the other leg of the L-shape beingconnected to the base with the hopper adjacent said inlet passage andincluding a plurality of sound minimizing curtains in said horizontallyextending leg attached to the top of the hopper and freely hangingdownwardly toward the bottom of the horizontal section of the hopper,said curtains comprising flexible sheets of an elastomer.
 6. Thestructure of claim 5 in which the layers of the outer composite wallcomprise in the order named from outside to inside: a layer of aluminum,a layer of artificial foamed plastic resin, a layer of lead, and a layerof artificial foamed plastic resin; and the layers of the innermostcomposite wall comprise, in the order named from outside to inside, alayer of vermiculite and a layer of steel, and said curtains comprise aplurality of pairs of curtains, each pair comprising two of said sheetshanging closely adjacent each other.
 7. A machine for cutting materials,comprising a base; cutting means mounted on the base; a motor fordriving the cutting means; inlet and exit passage means to and from thecutting means; a sound-absorbing combined enclosure and hopperstructure, said structure comprising: an elongated tubular structurehaving outside and inside composite walls, the walls being spaced apartto provide an airspace therebetween, the outer walls forming theenclosure and the inside walls forming the hopper, and including meansholding the walls in their spaced relation whereby the combined outsideand inside walls are adapted to move together; the outer composite wallbeing a plural-layered structure comprising an outermost first layer ofsound attenuation material and inner layers of sound-absorption materialand sound attenuation material; the inner composite wall comprising atleast two layers of material, a first innermost layer being of awear-resistant metal, and a second outer layer being a sound dampinglayer, the two layers being attached to each other; and said tubularstructure being movably hinged to said base with the inner end of saidhopper being located adjacent the mouth of said inlet passage, thestructure being movable on said hinge to swiNg away from said inletpassageway and said cutter, thereby to permit access to the latter. 8.The machine of claim 7 including a bin removably fastened to said baseadjacent said exit passage in position to receive material emergingtherefrom, and sound-absorbing means forming a gasket between the edgesof said bin and said base.
 9. The machine of claim 7 in which said motorhas a shaft and a pulley mounted thereon, said cutting means has a shaftand a pulley mounted thereon, and including a transmission beltconnecting said pulleys, and also including a shroud for said belt andfor said pulleys, said shaft passing through one wall of the shroud, andsound-absorbing material snugly fitted between the end of the frame ofthe motor and the wall of said shroud where the shaft passes through thewall, thereby to prevent the egress of sound from the interior of saidshroud to the outside thereof.
 10. The machine of claim 7 in which thecombined enclosure and hopper structure is generally L-shaped andvertically oriented, one leg of the structure extending generallyhorizontally and the other leg of the structure extending generallyvertically and being connected to said base with the hopper adjacentsaid inlet passage, the machine including a plurality of soundminimizing curtains in said horizontally extending leg, the curtainsbeing attached to the top of the hopper and freely hanging downwardlytoward the bottom of the horizontal section of the hopper.
 11. Themachine of claim 10 in which at least one of said curtains comprising aflexible sheet of synthetic plastic impregnated with lead particles, andat least one other of said curtains comprising two flexible layers ofsheet elastomeric material attached to the top of the hopper and hangingdownwardly adjacent each other.
 12. The structure of claim 7 in whichthe layers of the outer composite wall comprise in the order named fromthe outside to inside; a layer of aluminum, a layer of artificial foamedplastic resin, a layer of lead, and a layer of artificial foam plasticresin; and layers of the innermost composite wall comprise, in the ordernamed from outside to inside, a layer of sound attenuating material anda layer of steel.